Embodiments of the present invention relate to the field of image processing, and more particularly to the field of matching images against each other for identifying images having been derived from an original image by various image manipulation procedures such as cropping, resizing, altering brightness or contrast and the like.
In a number of technical fields, the ability to identify an image as being a derivative of another image may be of great practical importance. For example, the field of data leakage prevention may try to ensure that confidential data, e.g. images comprising personal, medical or otherwise confidential data, is protected from intentionally or unintentionally leaving the company, e.g. by means of an e-mail. Accordingly, it may be advantageous to reliably prohibit the leakage of digital assets of a company such as images of a new product design, company artwork, construction plans, personnel organigrams, and the like.
A common problem of corresponding image processing algorithms is that they can be computationally expensive and may slow down the data exchange over a network. In addition, many of those algorithms have difficulties in accurately identifying an image as a derivative of an original image in case an image manipulation technique or even a combination of multiple image manipulation techniques was applied in order to obtain the derivative image. Such image manipulations may be, for example, adjustments to brightness and contrast, color depth reductions, cropping, removing a copyright notice and so on. A further problem is related to the accuracy of state-of-the-art approaches for identifying derivative images: if an algorithm produces too many false-positive results, it may block important messages from leaving the company although the blocked image was not a derivative of a secret original image. In case an algorithm produces too many false negative results, it cannot reliably protect a company from data leakage.
U.S. Pat. No. 6,594,386 discloses a method for classifying images based on spatial distribution of color and color related features. The disclosed method is based on evaluating pixels of a window of a fixed size. U.S. Pat. No. 6,826,316 discloses a method for automatically providing perceptually significant features of the main subject or background of a first image. The method compares said features of a first image to perceptually significant features of the main subject or background of a second image. The method is based on segmenting images into a plurality of regions of homogeneous color and texture. In U.S. Patent Application Pub. No. 2008/0267519, a method is disclosed for searching an image repository containing a large number of images in order to identify distorted versions of a searched image. U.S. Pat. No. 7,856,144 provides for an image retrieving apparatus for determining a similarity between a feature amount matrix of a query image and a feature amount matrix of an image stored in a storage unit.